1. Field
Embodiments relate to an ultrasonic probe which uses a capacitive micromachined ultrasonic transducer (cMUT).
2. Description of the Related Art
An ultrasonic diagnosis apparatus irradiates ultrasound toward a target region of the interior of a body of an object from the surface of the object, and non-invasively acquires an image which relates to soft tissue tomograms or a blood stream by receiving a reflected ultrasonic signal (i.e., an ultrasonic echo signal).
The ultrasonic diagnosis apparatus is small and inexpensive, executes display in real time and has high safety without radiation exposure, as compared to other image diagnosis apparatuses, such as an X-ray diagnosis apparatus, an X-ray computerized tomography (CT) scanner, a magnetic resonance imager (MRI), and a nuclear medicine diagnosis apparatus, and is thus widely used for heart diagnosis, celiac diagnosis, urinary diagnosis, and obstetrical diagnosis.
The ultrasonic diagnosis apparatus includes an ultrasonic probe which transmits an ultrasonic signal toward an object and receives an ultrasonic echo signal which is reflected by the object, which received ultrasonic echo signal may be used to acquire an ultrasonic image of the object.
In general, a piezoelectric material that generates ultrasound by converting electrical energy into mechanical energy is widely used as a transducer generating ultrasound in an ultrasonic probe.
In recent years, a capacitive micromachined ultrasonic transducer (cMUT) has been developed as a new concept in the field of ultrasonic transducers.
The cMUT that is a relatively new concept in the field of ultrasonic transducers which transmit and receive ultrasound by using vibrations of hundreds or thousands of micro-processed thin films is manufactured based on micro electro mechanical system (MEMS) technology. A capacitor is formed by forming a lower electrode and an insulating layer on a semiconductor substrate commonly used in semiconductor manufacturing processes, forming an air gap on the insulating layer including the lower electrode, forming a thin film with a thickness of several to thousands of angstroms on the air gap, and forming an upper electrode on the thin film.
When an alternating current (AC) signal is applied to the capacitor, ultrasonic waves are generated by vibration of the thin film. Conversely, when the thin film is caused to vibrate by external ultrasonic waves, the capacitance of the cMUT varies. By detecting such capacitance variation, ultrasonic waves are detected.
Because one cMUT has a diameter of dozens of micrometers (μm), an array of tens of thousands of cMUT has a size which is on the order of approximately several millimeters. In addition, because tens of thousands of sensors may be accurately aligned at desired positions via a single semiconductor manufacturing process, and cMUT elements may be bonded to application-specific integrated circuits (ASICs) by chip bonding, such as flip-chip bonding, in order to apply electrical signals to the cMUTs, process complexity due to wiring may be overcome.
These features of the cMUT are suitable for a manufacture of a transducer which has a two-dimensional (2D) array, and may facilitate development of multi-channel transducers.
However, while an amount of heat which is generated in electrical circuits which are designed for driving an ultrasonic probe which includes a relatively small number of transducers is approximately equal to one watt (i.e., 1 W), which may be easily released via a probe case, heat which is generated in electrical circuits which are designed for driving an ultrasonic probe which includes multi-channel transducers is approximately equal to 7 W. Thus, there is a need to develop techniques to dissipate heat from the ultrasonic probe and cool the ultrasonic probe.